A 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system includes two modes: frequency division duplex (FDD) and time division duplex (TDD). In an FDD system, sending and receiving are performed on separate frequency channels. In a TDD system, sending and receiving are performed on one frequency channel, but sending and receiving are temporally separated, that is, different timeslots of a same frequency carrier are used for sending and receiving. The TDD system supports different uplink-downlink time configurations. An uplink-downlink time configuration may be adjusted according to different service types, so as to meet a requirement of an uplink-downlink asymmetric service.
In the releases 3GPP LTE Rel10/11, a carrier aggregation (CA) technology, also referred to as a spectrum aggregation technology or a bandwidth extension technology, is introduced to meet a peak data rate requirement of International Telecommunication Union on a fourth generation communication technology. During carrier aggregation, spectrums of two or more component carriers are aggregated to obtain wider transmission bandwidth. The spectrums of the component carriers may be adjacent continuous spectrums, or may be non-adjacent spectrums in a same frequency band or even discontinuous spectrums in different frequency bands. LTE Rel-8/9 user equipment (UE) can access only one component carrier to send and receive data, while LTE-A user equipment can access, according to its capability and a service requirement, multiple component carriers at the same time to send and receive data.
In an existing carrier aggregation system, aggregation is performed on carriers corresponding to a same evolved NodeB (eNB), or aggregation is performed on carriers of a macro cell and a micro cell between which an ideal backhaul link (Backhaul) exists, for example, the macro cell and the micro cell are connected by using an optical fiber (in this case, the micro cell may also be a radio-frequency head). In an existing CA system, hybrid automatic repeat request-acknowledgement information is sent only over a primary component carrier. In the existing CA system, duplex modes of aggregated carriers are the same, for example, may be FDD or may be TDD. In the existing CA system, if a duplex mode of a carrier is FDD, content of a DCI format of a downlink control channel corresponding to the carrier is determined in FDD mode; if a duplex mode of a carrier is TDD, content of a DCI format of a downlink control channel corresponding to the carrier is determined in TDD mode.
In a subsequent LTE system, carrier aggregation may evolve into aggregation in different duplex modes and/or aggregation between base stations. For aggregation in different duplex modes and/or aggregation between base stations, a problem of transmission of control information such as downlink control information and uplink control information needs to be resolved.